This invention relates to a continuous wet-laid process for making high-strength glass fiber mats.
High-strength, thin sheets or mats formed of glass fibers are finding increasing application in the building materials industry, as for example, in asphalt roofing shingles and as backing sheets for vinyl flooring. These glass fibers are replacing similar sheets made traditionally of organic or asbestos fibers. Such glass fiber mats may be made by the so-called "wet-laid process" on modified papermaking machinary as described in O. A. Battista, Synthetic Fibers in Papermaking, Wiley, (N.Y.) 1964 or in U.S. Pat. No. 3,905,067. However, since glass fiber mats useful for these building materials applications are relatively long by paper-making standards, normal processing in such equipment has presented numerous difficulties. In particular, such long fibers tend to rope or entangle when mixed or pumped during processing. To minimize this tendency it is necessary that expensive chemical additives be included in the process water. However, the additives may be more costly than the glass fibers themselves, and thus this solution to the problem is rather uneconomical. Another approach is to reduce the fiber consistency of the fiber dispersion being processed to a very low value. This prevents excessive entanglement of the fibers, but requires large volumes of water relative to the weight of the fibers themselves. Moreover, the excess water substantially increases the power consumption for the batch mixing and pumping of the water in the process. Furthermore, large tanks provided with expensive agitation equipment are necessary to prepare the initial fiber dispersion, and the rate of production of the mat is low, indeed.